The present invention relates to a phosphor material and a phosphor material powder that emit light with a high efficiency, a plasma display panel used in display devices and a method of producing the same.
The CRT has been commonly used as the display device for television sets. The CRT, although better in resolution and picture quality than the plasma display panel and the liquid crystal display, is not suited to large screens having diagonal size of 40 inches or more for the reason of depth size and weight. The liquid crystal display is limited in the screen size and the viewing angle, in spite of such advantages as the low power consumption and low drive voltage.
The plasma display panel, on the other hand, can be used in a large-screen display because there is no problem of depth size and weight, and 40-inch class products using the plasma display panel have already been developed (for example, see Functional Materials, February issue, 1996, Vol. 16, pp. 2, 7).
Constitution of a plasma display panel of the prior art will be described below with reference to the accompanying drawing. FIG. 23 is a sectional view showing schematic constitution of the AC type plasma display panel.
In FIG. 23, numeral 41 denotes a front cover plate (front glass substrate) with a display electrode 42 formed on the front glass substrate 41. The front cover plate 41 with the display electrode 42 formed thereon is also covered by a dielectric glass layer 43 and a protective layer 44 made of magnesium oxide (MgO) (see, for example, Unexamined Patent Publication (Kokai) No. 5-342991).
Numeral 45 denotes a back plate (back glass substrate), with an address electrode 46, barrier rib 47 and spherical phosphor layer 48 being provided on the back glass substrate 45, and numeral 49 denotes an electric discharge space filled with a discharge gas. The phosphor layer comprises phosphor layers of three colors, red, green and blue, disposed in this order for color display. The phosphor layers of different colors are excited to emit light by ultraviolet rays of short wavelength (147 nm) emitted by electric discharge.
As the phosphor layer 48 of the plasma display panel, (YGd)BO3:Eu is used for red, BaMgAl10O17:Eu is used for blue and Zn2SiO4:Mn is used for green today (for example, Electronics Packaging Technology; July, 1997; Vol. 113, No. 7, pp. 23-26).
The plasma display panels of 40- to 42-inch class described above that are produced at present have luminance of 150 to 250 cd/m2 at the pixel level of NTSC (640xc3x97480 pixels, cell pitch 0.43 mmxc3x971.29 mm, area of one cell 0.55 mm2) (for example, refer to Functional Materials, February issue, 1996, Vol. 16, pp. 2, 7). Recently, plasma display panels of 40- to 42-inch class having luminance of 250 to 450 cd/m2 at the pixel level of NTSC have also been reported (for example, see Flat Panel Display, 1997, Part 5-1, pp. 198-199). The conventional CRT technology is said, by contrast, to be capable of achieving a luminance of about 500 cd/m2.
The high-definition television of full specification that is at the focus of attention recently requires 1920xc3x971125 pixels, resulting in a resolution as fine as cell pitch of 0.15 mmxc3x970.48 mm and cell area of 0.072 mm2 in the case of 42-inch class. When a high-definition television set is produced with 42-inch plasma display panel, screen area per one pixel become as small as {fraction (1/7)} to xe2x85x9 that of the NTSC display. As a result, when the high-definition television set is produced with the 42-inch plasma display panel of the conventional cell configuration, emission intensity of the display panel becomes {fraction (1/7)} to xe2x85x9 that of the NTSC display, namely 0.15 to 0.171 m/W.
Thus luminance of a high-definition television produced with the 42-inch plasma display panel is predicted to be as low as 30 to 40 cd/m2, given the same phosphor, gas composition and gas pressure, making it desirable to improve the luminance.
As described above, when a television set of such a small pixel size as in the high-definition television is produced using the plasma display panel with similar brightness, luminance must be greatly increased.
There are also such problems as described below with regard to phosphor material.
The first problem is that phosphor materials of different colors have different levels of luminance.
While several types of phosphor have been investigated for each of red, green and blue light in the plasma display panel, green phosphor has the highest luminance and blue phosphor has the lowest luminance in any of these types.
For example, when YBO3:Eu is used as the red phosphor, Zn2SiO4:Mn is used as the green phosphor and BaMgAl10O17:Eu is used as the blue phosphor (Eu content 0.15), luminance ratio of the colors of red, green and blue is about 2:3:1, with a low color temperature of about 5000 degrees.
Accordingly in the plasma display panel of the prior art, color temperature is increased by electronically suppressing the light emission by the green phosphor that has high luminance, thereby to improve the white balance. However, this configuration leads to lower brightness of the plasma display panel as a whole due to the reduction in the emission of light from the phosphor having high luminance.
This indicates that increasing the luminance of blue light is very effective in solving the problem, since color temperature can be increased without reducing the luminance of green and red light by increasing the luminance of blue light that is the lowest of the phosphors.
Second, phosphor layers of the plasma display panels of the prior art are formed by applying an ink that contains phosphor particles by a printing process or coating a photosensitive sheet that contains phosphor particles. In either of these processes, it is necessary to fire the panel at a temperature of around 500xc2x0 C. after forming the phosphor layer, in order to remove an organic binder component included in the ink or the sheet. It is also necessary to fire the panel at a temperature of 400xc2x0 C. or higher to have the front cover plate and the back plate bonded with each other.
In these firing processes, the phosphors used in the panel are subject to a certain extent of thermal change that results in degradation of luminance and/or chromaticity.
As described above, the plasma display panel has the problem of the thermal deterioration of the phosphor material in the firing process that are required for the production (for example, Transaction of the 263rd Conference of Phosphor Engineering Association, pp. 9-13, 1996; Optonics, 1997, No.6, pp. 149-155).
In the firing processes, the phosphors are subject to a certain extent of thermal change that results in degradation of luminance and/or chromaticity. Ba(1-x)MgAl10O17:Eux used as the blue phosphor at present experiences particularly significant thermal deterioration.
The Ba(1-x)MgAl10O17:Eux used as the blue phosphor can easily be damaged by vacuum ultraviolet rays (wavelength 147 nm, 172 nm) that excite the plasma display panel, and the emission intensity decreases as the panel is operated longer, thus giving rise to a problem of service life.
As described above, the blue phosphor material of the plasma display panel has the problems of thermal deterioration of the phosphor material in the firing processes required for the producing and short service life.
There have been efforts being made to mitigate the thermal deterioration of the phosphor.
For example, the Optical Technology Contact, Vol. 34, No. 1 (1996) pp. 23-24 reports that the BaMgAl10O17:Eu2+ that had been known as an excellent blue phosphor showed such problems as deterioration during operation of the panel and change in chromaticity, and that BaMgAl10O17:Eu2+ was developed to solve such problems with an improvement achieved in mitigating the decrease in luminance caused by firing in the panel producing process.
As demands for high quality display increase, however, such technologies are required that prevents the deterioration of the luminance and of chromaticity of the phosphor layer and improve the emission intensity (luminance divided by the y value of chromaticity) in order to improve the luminance and picture quality of the plasma display panel.
First object of the present invention is to provide a phosphor material and a phosphor material powder of high luminance, particularly a phosphor material and a phosphor material powder that are suited to a plasma display panel and a method of producing the same.
Second object of the present invention is to provide a plasma display panel having high luminance and high reliability.
The first plasma display panel of the present invention has, for the purpose of achieving the first object described above, a plurality of discharge spaces formed between a front panel and a back panel that are disposed to oppose each other, and phosphor layers, formed in the discharge spaces, each including phosphor particles of one of blue, red and green colors, wherein the phosphor particles of at least one of blue, red and green colors included in the phosphor layer are flake-like particles.
Phosphors used in the plasma display panel of the prior art have generally made by firing for a long period of time at high temperatures (for example, 1200xc2x0 C. though the firing temperature depends on the composition of the phosphor) at which crystals are likely to grow into spherical shape. As a result, the phosphor particles used in the plasma display panel of the prior art have been of near spherical shape having large diameters (about 5 to 10 xcexcm). Such phosphor particles of near spherical shape have been advantageous in transmission type devices such as CRT and fluorescent lamp where visible light must be transmitted between the phosphor particles.
In the plasma display panel, however, since it is a reflection type panel in which fluorescence is generated by ultraviolet rays of short wavelengths (147 nm, 173 nm) emitted by electric discharge and the fluorescent light is emitted in the direction opposite to the incident direction of the ultraviolet rays, use of the phosphor particles of near spherical shape results in lower coverage ratio of the barrier ribs and the base of the barrier rib, thus making it impossible to make full use of the ultraviolet rays. Coverage ratio in this specification refers to an index that represents the proportion of the surface of the walls covered by the phosphor material or the phosphor particles to the total area of wall surface whereon the phosphor layer is formed. As the coverage ratio increases, higher proportion of the light incident on the phosphor layer is absorbed by the phosphor material and the phosphor particles.
When flaky phosphor particles, namely particles of thin and flat shape of which breadth is far greater than the thickness are used, as in the case of the first plasma display panel of the present invention, the barrier ribs and the base in the phosphor layer are covered by the phosphor particles with higher coverage ratio, which increases the proportion of ultraviolet rays absorbed in the phosphor layer. As a result, higher luminance than the prior art can be achieved in the first plasma display panel of the present invention. Also because ultraviolet rays having wavelength of 143 nm or 173 nm can penetrate only through the superficial portion of the phosphor layer exposed to the discharge space (to depth not greater than 0.1 xcexcm) unlike electron beams used in the CRTs (refer to, for example, monthly xe2x80x9cLCD Intelligencexe2x80x9d, September, 1996, pp. 58), the constitution of the present invention that increases the percentage of loading and coverage ratio of the phosphor layer with the phosphor particles is very effective in absorbing much of the ultraviolet rays in the superficial portion of the phosphor layer.
Also because the percentage of loading and coverage ratio of the phosphor layer with the phosphor particles can be increased in the first plasma display panel of the present invention, emission intensity of the phosphor layer can be increased. Moreover, since the phosphor particles themselves act as reflectors for visible light, increasing the percentage of loading by phosphor increases the luminance of reflection at the same time. This effect is made conspicuous when the flaky phosphor particles are used in the phosphor layers of every color.
In the first plasma display panel of the present invention, as described above, since the phosphor layers that include the flaky phosphor particles are formed, efficiency of absorbing ultraviolet rays in the phosphor layer can be increased and thereby increasing the luminance of the plasma display panel.
Such flaky phosphor particles as described above can be easily made changing the firing conditions, starting materials or atmosphere of firing when making the phosphor. Specifically, phosphor particles that have better crystallizability in the very superficial portion of the phosphor layer and a higher profile ratio (breadth/thickness) can be obtained by setting the firing temperature somewhat higher and performing the firing for a shorter period of time.
Blue and green phosphor particles can be relatively easily made in a shape of hexagonal flake because these substances have hexagonal system of crystalline structure (see, for example, Phosphor Handbook, Ohm Publishing Co., pp. 219, pp. 225). Red phosphor particles, however, have cubic system and are therefore difficult to make in flaky shape. However, it becomes relatively easy to make red phosphor particles of flaky shape by using yttrium hydroxide (Y2(OH)3) as the starting material.
When the flake of the phosphor particle is too thin or too small in breadth, however, the phosphor particles coagulate resulting in lower luminance on the contrary to the intention. Therefore, in order to make a plasma display panel of higher luminance, it is preferable for the first plasma display panel of the present invention, according to our study, to set the breadth and thickness of the flakes of phosphor particles as follows, although it depends on the color.
The blue phosphor particles described above may comprise flaky particles based on a phosphor represented by general formula of Ba(1-x)EuxMgAl10O17 (0.03xe2x89xa6xxe2x89xa60.25) as the major component, while preferably the breadth thereof is in a range from 0.3 to 6 xcexcm, thickness is in a range from 0.1 to 2 xcexcm, and profile ratio (breadth/thickness) is in a range from 3 to 25.
The phosphor represented by the general formula Ba(1-x)EuxMgAl10O17 is a phosphor represented by BaMgAl10O17Eu2+.
The green phosphor particles may comprise flaky particles made of a phosphor represented by a general formula of (Zn1-xMnx)SiO4. (0.01xe2x89xa6xxe2x89xa60.05) as the major component, while preferably the breadth thereof is in a range from 0.3 to 6 xcexcm, thickness is in a range from 0.1 to 2 xcexcm, and profile ratio (breadth/thickness) is in a range from 3 to 25.
The phosphor represented by the general formula Zn1-xMnx)SiO4 is represented as Zn2SiO4:Mn2+.
The red phosphor particles may comprise flaky particles made of a phosphor represented by a general formula of Y1-xEuxBO3 (0.05xe2x89xa6xxe2x89xa60.15) as the major component, while preferably the breadth thereof is in a range from 0.5 to 6 xcexcm, thickness is in a range from 0.2 to 2 xcexcm, and profile ratio (breadth/thickness) is in a range from 2.5 to 15.
The phosphor represented by the general formula Y1-xEuxBO3 is a material represented by YBO3:Eu3+.
The phosphor particles having a high profile ratio as described above are preferably made by adding a somewhat greater amount of activation agent in order to ensure sufficient number of luminance centers for the amount of ultraviolet rays absorbed.
Also in the first plasma display panel of the present invention, the discharge space can be formed on the back panel by partitioning the surface with barrier ribs that are formed by plasma spraying. The phosphor layers can be formed on the barrier ribs and on the bottom surface of the discharge space by firing after continuously discharging the phosphor ink, that includes the phosphor particles, a solvent and a resin binder, from a nozzle and then drying.
In the first plasma display panel of the present invention, the barrier ribs preferably comprise a first layer made of one white material selected from among a group consisting of alumina (Al2O3), spinel (MgO.Al2O3) and zircon (ZrO2) and a second layer made of a black material selected from among a group consisting of chromium oxide (Cr2O3), alumina titania (Al2O3xe2x80x94TiO3), chromium oxide-cobalt oxide (Cr2O3xe2x80x94CoO), chromium oxide-manganese oxide (Cr2O3xe2x80x94MnO2), and chromium oxide-iron oxide (Cr2O3)xe2x80x94Fe2O3).
A plasma display panel of even more higher luminance and higher display contrast can be obtained by using the flaky phosphor particles and coating the area between the barrier ribs that are black-colored on the upper portion (second layer) with the particles by ink jet-process (application of the ink by continuously discharging the ink from a fine tube).
A method of producing the first plasma display panel of the present invention is a method of producing a plasma display panel comprising a plurality of discharge spaces formed between the front panel and the back panel disposed to oppose each other, and phosphor layers that are formed in the discharge spaces and include phosphor particles of one of blue, red and green colors, wherein the phosphor layers are formed by spraying the phosphor ink that includes the phosphor particles, the solvent, a resin binder and a dispersion agent from the nozzle.
In the method of producing the first plasma display panel, it is preferable to control the viscosity of the phosphor ink within a range from 15 to 1000 centipoise.
In the method of producing the first plasma display panel, it is also preferable to use ethyl cellulose or acrylic resin for the resin binder.
A first phosphor material according to the present invention is a blue phosphor material for the plasma display panel, one selected from a group consisting of a phosphor represented by general formula Ba(1-x)EuxMgAl10O17, a phosphor represented by general formula Ba2(1-x)Eu2xMg2Al12O22, a phosphor represented by general formula Ba2(1-x)Eu2xMg4Al8O18 and a phosphor represented by general formula Ba3(1-x)Eu3xMg5Al18O35, where value of x is limited as 0.01xe2x89xa6xxe2x89xa60.15, and has a laminar structure
The material represented by BaMgAl10O17:Eu that has been used as the blue phosphor is a laminar compound having xcex2-alumina structure or magnetoplumbite structure (see, for example, Phosphor Handbook, Ohm Publishing Co., Dec. 15, 1987, pp. 225)
This conventional blue phosphor material has such a crystal structure as a layer including barium (Ba) (R layer) and a layer without barium (Ba) (spinel layer, S layer) are arranged alternately one on another (plate crystal), wherein europium ion (Eu2+) that serves as the luminescence center is substituted at the lattice position of Ba ion (Eu ions are not substituted in the spinel layer).
The present inventors completed the first phosphor material base on the assumption that luminance increases as the layer containing europium ion (Eu2+) that serves as the luminescence center (layer containing Ba) is made in such a crystal system that exists with a high concentration in the xcex2-alumina structure. Specifically, the first phosphor material of the present invention is made in such a composition that the blue phosphor material for the plasma display panel employs a crystal system of xcex2-alumina or magnetoplumbite structure such as Ba2Mg4Al8O18, Ba3Mg5Al18O35 or Ba2Mg2Al12O22 as the base material, where there are more layers that include Ba than in the base material based on BaMgAl10O17:Eu used in the prior art, and improved in the luminance by substituting Ba of these crystals with Eu.
The second plasma display panel of the present invention has a plurality of discharge spaces formed between the front panel and the back panel disposed to oppose each other, and the phosphor layers that include phosphor particles of one of blue, red and green colors and are formed in the discharge spaces.
The blue phosphor that constitutes the phosphor layer described above is one or more kinds of phosphor selected from a group consisting of a phosphor represented by general formula Ba(1-x)EuxMgAl10O17, a phosphor represented by general formula Ba2(1-x)Eu2xMg2Al12O22, a phosphor represented by general formula Ba2(1-x)Eu2xMg4Al8O18 and a phosphor represented by general formula Ba3(1x)Eu3xMg5Al18O35, with the condition of 0.01xe2x89xa6xxe2x89xa60.1.
In the material represented by BaMgAl10O17:Eu used as the blue phosphor of the prior art, the amount of Eu ions serving as the luminescence center that substitute the Ba ions in the Ba layer is usually set around 10 to 15 atomic percent, unlike in the case of the blue phosphor used in the second plasma display panel.
This is because, though the initial luminance increases as the substitution ratio by Eu2+ ions is increased (for example, National Technical Report Vol. 43, No. 2, April 1997, pp. 70), the luminance decreases in the phosphor firing process (500 to 600xc2x0 C.) when the content of Eu ions exceeds 10 atomic % and therefore substitution ratio by Eu2+ ions is set around 10 atomic % to 15 atomic % (for example, OPTRONICS, 1997, No. 6, pp. 154).
However, it was found through our research that it is important to evaluate the picture quality of the display panel in terms of chromaticity as well as luminance, and it is important to evaluate the emission intensity (luminance divided by the y value of chromaticity) that includes both of these parameters.
When compared in terms of the emission intensity, comparable values are obtained after firing at a temperature around 500xc2x0 C. with substitution of within 10 atomic %. In the plasma display panel, further firing at a temperature around 400xc2x0 C. is required in order to bond the front and back panels. By setting the substitution ratio by Eu2+ ions in this process to such a level as in the configuration of the present invention, it is made possible to achieve the phosphor layer having higher emission intensity than the phosphor layer of the prior art. Particularly when the substitution ratio by Eu2+ ions is set within 10 atomic % and not less than 1 atomic %, a display panel having high performance in terms of both luminance and chromaticity can be obtained. In the second plasma display panel of the present invention, based on these results, it is intended to prevent thermal deterioration of the blue phosphor in the phosphor firing process by limiting the proportion of the Ba ions that can be substituted with Eu ions within 10 atomic % of the Ba content.
As described above, use of the blue phosphor material of the present invention makes it possible to form the phosphor layer of high luminance and high heat resistance, being capable of suppressing thermal deterioration in the firing process during the production of the plasma display panel, and achieve the plasma display panel of high luminance and good picture quality.
The first phosphor material powder according to the present invention includes the phosphor particles and non-fluorescent white particles that have average particle size smaller than the average particle size of the phosphor particles mixed therein.
The phosphor material powder of the prior art comprises only the phosphor particles. In a phosphor layer formed from these phosphor particles, the percentage of loading of phosphor particles in the layer increases as the particle size of the phosphor becomes smaller and, as a result, the effect of reflection in the layer becomes greater thus making it possible to extract the emitted visible light efficiently through the front surface of the layer.
At the same time, however, specific surface area of the phosphor increases as the phosphor particles become smaller, that makes crystal defects more likely to occur which leads to deterioration of light emission characteristic, thus forming a tradeoff relationship.
When using such a phosphor material made by mixing the phosphor particles and non-fluorescent white particles that have average particle size smaller than the average particle size of the phosphor particles is used as the first phosphor material powder of the present invention, by contrast, efficient emission of light is achieved with phosphor particles of relatively large particle size. Moreover, when a layer is formed, percentage of loading is increased as the voids between the phosphor particles of relatively large particle sizes is filled with the non-fluorescent white particles of relatively small particle sizes, resulting in improved reflectivity in the layer and making it possible to extract the emitted light efficiently through the front surface of the layer.
In the first phosphor material powder of the present invention, average particle size of the phosphor particles is preferably in a range from 1.5 xcexcm to 5 xcexcm inclusive, and average particle size of the non-fluorescent white particles is preferably 1.5 xcexcm or smaller. It is also preferable that average particle size of the phosphor particles is twice that of the non-fluorescent white particles or larger.
The percentage of loading can be increased further by making average particle size of the phosphor particles five times or more larger than that of the non-fluorescent white particles.
With the average particle size of the phosphor particles denoted as A, minimum particle size thereof be dmin, maximum particle size be dmax and coefficient of particle size concentration be x (%) with x being calculated as x=100A/(A+dmaxxe2x88x92dmin), it is preferable to make the coefficient of particle size concentration of the particle size distribution of at least either the phosphor particles or the non-fluorescent white particles not less than 50% within 100%, which makes it possible to effectively fill the voids between the larger phosphor particles with the smaller non-fluorescent white particles.
The percentage of loading can be increased further by setting the coefficients of particle size concentration of the phosphor particles and the non-fluorescent white particles in a range from 80% to 100% inclusive.
In order to increase the percentage of loading further, total number of the non-fluorescent white particles is preferably less than the total number of the phosphor particles.
The phosphor particles described above may also be a blue phosphor represented by general formula Ba1-xEuxMgAl10O17.
The phosphor particles described above may also be a green phosphor represented by general formula (Zn1-xMnx)SiO4.
The phosphor particles may be a green phosphor represented by general formula Ba1-xMgxAl12O19.
The phosphor particles may also be a red phosphor represented by general formula Y1-xEuxBO3.
The phosphor particles may also be a red phosphor represented by general formula Y1-x-yGdxEuyBO3.
The percentage of loading can also be increased by using the phosphor particles or the non-fluorescent white particles that are spherical or substantially sphere-shaped particles.
It is also effective to use Al2O3 or TiO2 that has high reflectivity for visible light as the non-fluorescent white particles.
The third plasma display panel of the present invention has a plurality of discharge spaces formed between a front panel and a back panel disposed to oppose each other, with a phosphor layer that includes phosphor particles of one of blue, red and green colors being formed in each of the discharge spaces, while the phosphor layers include the first phosphor material powder of the present invention. In the third plasma display panel that uses the first phosphor material powder of the present invention as described above, the percentage of loading of the phosphor material powder in the phosphor layer can be increased thus giving the layers good reflective characteristics. Thus it is made possible to extract the visible light emitted by the phosphor efficiently through the entire surface of the panel, and increase the luminance and the emission efficiency.
In third plasma display panel of the present invention, thickness of the phosphor layers is preferably in a range from 5 xcexcm to 50 xcexcm.
The second phosphor material powder of the present invention is an aggregate of phosphor particles, and is characterized in that the number of phosphor particles having particle sizes not less than the peak particle diameter Dp is less than the number of phosphor particles having particle sizes not greater than the peak particle diameter Dp, with Dp representing the peak particle diameter in the particle size distribution of the phosphor particles.
Conventional phosphor material powder generally has a nearly symmetrical particle size distribution with the peak particle size at the center thereof. The phosphor layer that includes the phosphor material powder has higher reflecting effect inside the layer when the percentage of loading is higher, thus making it possible to extract the emitted visible light effectively through the front surface of the layer. The second phosphor material of the present invention is made by reducing the number of relatively large particles in the particle size distribution to achieve the such a particle size distribution as described above, thus making it possible to fill the voids between the phosphor particles with smaller phosphor particles more densely, and extract the emitted visible light efficiently through the front surface of the layer.
In the second phosphor material powder of the present invention, the number of phosphor particles having particle sizes not less than peak particle diameter Dp is preferably within 70% of the number of phosphor particles having particle sizes not greater than the peak particle diameter Dp.
In the second phosphor material powder of the present invention, the number of phosphor particles having particle sizes not less than the peak particle diameter Dp is more preferably within 50% of the number of phosphor particles having particle sizes not greater than peak particle diameter Dp, which enables it to improve the percentage of loading further.
The second phosphor material powder of the present invention is an aggregate of phosphor particles, and is prepared to have such a particle size distribution as Dmaxxe2x88x92Dp is less than Dpxe2x88x92Dmin, with Dp representing the peak particle diameter, Dmin the minimum particle size and Dmax the maximum particle size of the phosphor particles.
In the second phosphor material powder of the present invention, the particle size distribution is preferably such as (Dmaxxe2x88x92Dp) is less than 0.5 times the value of (Dpxe2x88x92Dmin).
In the second phosphor material powder of the present invention, the particle size distribution is preferably such that (Dmaxxe2x88x92Dp) is less than 0.3 times the value of (Dpxe2x88x92Dmin). This enables it to improve the percentage of loading of the phosphor particles further.
In the second phosphor material powder of the present invention, peak particle diameter Dp of the particle size distribution of the phosphor particles is preferably from 1.5 xcexcm to 5 xcexcm inclusive.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise such a phosphor that the phosphor particles emit visible light upon excitation by ultraviolet rays.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise blue phosphor material represented by general formula Ba(1-x)EuxMgAl10O17.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise a green phosphor material represented by general formula of (Zn1-xMnx)SiO4.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise a green phosphor represented by general formula Ba1-xMgxAl12O19.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise a red phosphor represented by general formula Y1-xEuxBO3.
In the second phosphor material powder of the present invention, the phosphor particles may also comprise a red phosphor represented by general formula Y1-x-yGdxEuyBO3.
In the second phosphor material powder of the present invention, the phosphor particles have preferably spherical or near spherical shape, which enables it to improve the percentage of loading further.
The fourth plasma display panel of the present invention has a plurality of discharge spaces formed between a front panel and a back panel disposed to oppose each other, with a phosphor layer that includes phosphor particles of one of blue, red and green colors being formed in each of the discharge spaces, while the phosphor layers include the second phosphor material powder of the present invention. Thus the percentage of loading of the phosphor material powder in the phosphor layer can be increased giving the layers good reflective characteristics. This makes it possible to extract the visible light emitted by the phosphor efficiently through the entire surface of the panel, and make a plasma display panel of high luminance and high emission efficiency.
In the fourth plasma display panel of the present invention, thickness of the phosphor layer is preferably in a range from 5 xcexcm to 50 xcexcm inclusive.
The second phosphor material of the present invention is represented by general formula Ba(1-x-y)SryMgaAlbOc:Eux, where the value of x is in a range from 0.01 to 0.08 inclusive.
In the phosphor material such as Ba(1-x)MgAl10O17:Eux used for the blue phosphor in the prior art, value of x that represents substitution ratio by Eu2+ ions is generally in a range from 0.1 to 0.15.
This is because the highest luminance can be achieved when the value of x is in a range from 0.1 to 0.15 after firing at a temperature around 500xc2x0 C., because the heat resistance tends to increase as the substitution ratio by Eu2+ ions decreases, although the initial luminance increases as the substitution ratio by Eu2+ ions is increased.
With respect to the picture quality of the display panel, it is important to evaluate the chromaticity as well as the luminance, and accordingly it is important to evaluate the emission intensity (luminance divided by the y value of chromaticity) that includes both of these parameters
When compared by the emission intensity, substantially the same values are obtained after firing at a temperature around 500xc2x0 C. when the value of x is 0.1 or less.
The plasma display panel requires another firing process at a temperature around 400xc2x0 C. to bond the front and back panels, that causes deterioration in the emission intensity although this temperature of the second firing is lower than the phosphor firing temperature that is around 500xc2x0 C. A phosphor layer of higher emission intensity than that of the phosphor layer of the prior art can be achieved by setting the substitution ratio by Eu2+ ions as in the configuration of the present invention, thereby increasing the heat resistance. The present invention was completed by finding this fact.
In the second phosphor material of the present invention, the value of x is preferably in a range from 0.02 to 0.075 inclusive, and more preferably in a range from 0.03 to 0.06 inclusive.
Service life (ultraviolet radiation resistance) of the Ba(1-x)MgAl10O17:Eux generally increases as the substitution ratio by Eu2+ ions is increased. However, the service life and the heat resistance are in the relation of trade-off. Service life of the Ba(1-x)MgAl10O17:Eux can be increased by substituting a part of Ba with Sr. Therefore, when the substitution ratio by Eu2+ ions is decreased as in the second phosphor material of the present invention and substitution ratio by Sr is set as in the present invention at the same time, a phosphor of higher heat resistance and longer service life than the phosphor of the prior art can be obtained.
In the second phosphor material of the present invention, the value of y is preferably in a range from 0.01 to 0.2 inclusive, more preferably in a range from 0.02 to 0.15 inclusive and further more preferably in a range from 0.02 to 0.1 inclusive.
Moreover, the value of x+y is preferably in a range from 0.05 to 0.2 inclusive, and more preferably in a range from 0.09 to 0.15 inclusive.
In the second phosphor material of the present invention, the parameters in the general formula described above may be such as a is 1, b is 10 and c is 17, or alternatively a is 1, b is 14 and c is 23.
Further in the second phosphor material of the present invention, when applied to the plasma display panel, it is preferable that the phosphor emits visible light when excited by ultraviolet rays and more preferably emits visible light when excited by ultraviolet rays of wavelength 200 nm or less.
The fifth plasma display panel of the present invention has a plurality of discharge spaces formed between the front panel and the back panel disposed to oppose each other, with a phosphor layer that includes phosphor particles of one of blue, red and green colors being formed in each of the discharge spaces, while the phosphor layers that contain the blue phosphor particles include the second phosphor material powder of the present invention.
When the second phosphor material of the present invention is used, as described above, phosphor layers of high heat resistance and high durability can be formed while restraining thermal deterioration during the firing process and suppressing deterioration of the emission intensity when illuminating, thus making it possible to achieve a plasma display panel that has high emission intensity, long service life and high picture quality.
In the fifth plasma display panel of the present invention, the phosphor layers that contain the blue phosphor particles may be produced through at least one process of firing at a temperature of 400xc2x0 C. or higher.
In the fifth plasma display panel of the present invention, the phosphor layers that contain the blue phosphor particles may also be produced through at least one process of firing at a temperature of 500xc2x0 C. or higher.
In the fifth plasma display panel of the present invention, the phosphor layers that contain the blue phosphor particles may also be produced through at least two firing processes. In this case, firing temperature for the phosphor layers that contain the blue phosphor particles is preferably lower in the second firing process than in the first firing process.
The third phosphor material of the present invention is a phosphor material of which base material is partially substituted with Eu2+ ions, with the substitution ratio by Eu2+ ions being 8 atomic % or lower.
In the third phosphor material of the present invention, substitution ratio by Eu2+ ions is preferably in a range from 1 to 6 atomic %.
In the blue phosphor material wherein a certain element in the base material is substituted with Eu2+ ions that serve as deactivating agent, including a phosphor represented by general formula of BaMgAlyOz, the phosphors of substitution ratio by Eu2+ ions in a range from 10 to 15 atomic % have been used in the prior art.
With the third phosphor material of the present invention, luminance and emission intensity can be made higher than in the prior art by forming the phosphor layer using the phosphor material of the present invention. The invention was completed upon finding that picture quality and luminance of the plasma display panel can be improved by using such phosphor materials as the blue phosphor material.
With the third phosphor material of the present invention, as described above, it is made possible to form the phosphor layer having heat resistance higher than in the prior art and improve the luminance and emission intensity of the phosphor layer, by setting the Ba substitution ratio by Eu2+ ions within 8 atomic % or preferably in a range from 1 to 6 atomic % in the phosphor material in which the element to be substituted in the base material is substituted by Eu2+ ions, particularly a phosphor represented by the general formula of BaMgAl10O17:Eu2+.
Thus high luminance and high emission intensity can be achieved by setting the substitution ratio by Eu2+ ions to a low level as described above, even when the plasma display panel is produced by firing the panel after coating with the phosphor material thereby burning out the binder and forming the phosphor layer and then firing again in the panel sealing process, namely even when the phosphor material is subjected to firing twice.
The third phosphor material of the present invention preferably contains BaMgAlyOz as the base material with the substitution ratio of Ba by Eu2+ ions being set within 8 atomic % or preferably in a range from 1 to 6 atomic % also in this case.
Also in the third phosphor material of the present invention, values of y and z in the formula BaMgAlyOz of the base material are preferably 10 and 17, respectively.
The values of y and z in the formula BaMgAlyOz of the base material may also be 14 and 23, respectively.
The sixth plasma display panel of the present invention has a plurality of discharge spaces formed between the front panel and the back panel disposed to oppose each other, with a phosphor layer that include phosphor particles of one of blue, red and green colors being formed in each of the discharge spaces, while the blue phosphor particles included in the phosphor layers are made of the third phosphor material powder of the present invention.
When the third phosphor material of the present invention is used for the blue phosphor material, as described above, thermal deterioration of the phosphor layer can be suppressed in the firing process during production of the plasma display panel, thus making it possible to improve the picture quality and luminance of the plasma display panel.
A method for forming the phosphor layer according to the present invention is a method of forming the phosphor layer on a substrate, comprising a phosphor material applying step of applying the phosphor material together with a binder, wherein a part of Ba atoms of BaMgAlyOz of the base material are substituted with Eu2+ ions with the substitution ratio by Eu2+ ions being within 8 atomic %, and a firing step of firing the substrate whereon the phosphor material is applied.
The phosphor applying step of this forming method may be a process of coating the substrate with an ink or a sheet made by mixing particles of the phosphor material and the binder.
A second method of producing the plasma display panel according to the present invention comprises a phosphor applying step of applying the phosphor material together with the binder onto a first panel substrate, the phosphor material being such as a part of Ba atoms of BaMgAlyOz of the base material are substituted with Eu2+ ions with the substitution ratio by Eu2+ ions being in a range from 1 to 6 atomic %, a firing step of firing the first panel substrate whereon the phosphor material has been applied, and a sealing step wherein the first panel and the second panel are placed one on another and sealed following the firing step.
The phosphor applying step of the second producing method may be a process of applying the ink or the sheet made by mixing particles of the phosphor material and the binder onto the first panel substrate.
Further according to the second producing method, the sealing step may be a process of placing the first panel and the second panel are placed one on another via a sealing agent then firing and thereby sealing the assembly, following the firing step described above.